Start with d20 Modern
- Add WP/VP system to replace hit points
- After hearing myself rant on and on about how Strength really means coordination, get tired of being told that there's no book evidence for it. Take out Strength, separate Dexterity into Precision and Agility (a common-enough RPG differentiation point), with Agility modifying melee attacks, defense, initiative, and fast full-body skills like Tumble, and Precision modifying ranged attacks, slow full-body skills like Hide and Move Silently, and Fine-tuning skills like Disable Device. Use Constitution to determine bonuses to melee damage, since most folks have issue with the idea of a weak person who isn't frail, or a tough person who isn't strong.
- Change Armor to DR rather than Defense boosting